I have not found any test for the find_first_of algorithm. It was
declared in 25.find.cpp but was not exercised anywhere. So I implemented
this test - see it in the attached file, please.

Here I implemented our own predicate which may be used instead of
std::equal_to. I think it may be useful to update this predicate (if
necessary) and use it in other tests instead of std::equal_to.


With best wishes,
Anton Pevtsov